1. Field of the Invention
The present invention relates to hard disk drives and a method for minimizing wear patterns created by contact between a head and a disk of the drive.
2. Background Information
Hard disk drives contain a plurality of magnetic heads that are coupled to rotating disks. The heads write and read information by magnetizing and sensing the magnetic fields of the disk surfaces. Each head is attached to a flexure arm to create a subassembly commonly referred to as a head gimbal assembly (“HGA”). The HGA's are suspended from an actuator arm. The actuator arm has a voice coil motor that can move the heads across the surfaces of the disks.
The disks are rotated by a spindle motor of the drive. Rotation of the disks creates an air flow within the disk drive. Each head has an air bearing surface that cooperates with the air flow to create an air bearing between the head and the adjacent disk surface. The air bearing eliminates or minimizes the mechanical wear between the head and the disk. The height of the air bearing is commonly referred to as the fly height of the head.
The magnetic field detected by the head is inversely proportional to the fly height of the head. Likewise, the strength of the magnetic field written onto the disk is also inversely proportional to the fly height. A larger fly height will produce a weaker magnetic field on the disk.
There have been developed heads that contain a heater coil. Current is provided to the heater coil to generate heat and thermally expand the head to move the read and write elements closer to the disk. Heads with heater coils are sometimes referred to as fly on demand (“FOD”) heads. The fly height of FOD heads can be varied by changing the voltage applied to the heater coil.
To optimize the performance of a disk drive a calibration technique is typically employed to determine the correct voltage(s) that is to be applied to the heating elements of the heads. The calibration technique includes incrementing the heating element voltage until the head makes contact with the disk.
The disks are typically covered with an outer layer of lubricant to reduce friction between the heads and the disks. During the calibration technique the head may drag along the disk and create undesirable wear of the lubricant. FIG. 1 shows a disk track with a series of modulated wear patterns 1 caused by a calibration technique. The frequency of modulation typically corresponds to the first slider pitch mode of the head. For example, the wear pattern may have a frequency of 200,000 hertz. The modulated wear pattern can degrade head-disk interface reliability.